The invention relates to a protective screen for the screening off of a suction space and of a suction duct connected to it.
A reactor in a nuclear power plant is surrounded by a safety container of concrete and steel, the so-called containment. Furthermore, the reactor is equipped with an emergency cooling system (termed Emergency Core Cooling or ECC in English) in order to cool the reactor core in the event of a malfunction or incident. In such a case the water is sucked in from the lowermost part of the safety container, the so-called sump, by emergency cooling pumps via suction ducts and circulated through the reactor core.
In the design scenario for the emergency cooling system it is assumed that insulation debris and chunks of concrete which arise in an incident can fall down into the sump and/or be washed down into the sump by the downwardly flowing water. In order that the debris do not impair the ability of the emergency cooling system to operate, special screen elements, referred to as protective screens herein, are provided in front of the inlet openings of the suction ducts which lead to the emergency cooling pumps. These protective screens have the task of keeping back the debris resulting from the incident and simultaneously ensuring an adequate through-flow of water. In this connection it must be ensured that the pressure drop caused by the debris does not exceed the permissible limiting value.
Previously known protective screens used in nuclear power plants with pressure water reactors (PWR) are mainly formed as flat grid segments which have only a small screen surface and which in the event of contamination with fibrous debris materials produce an impermissibly high pressure drop. Protective screen elements of corrugated and perforated sheet metal offer a larger effective screen area. However, deformations occur under pressure loading which restrict the size of such protective screen elements. A cylindrical suction screen is described in EP 0 818 227 A1 which admittedly has a very large effective screen area but can only be used in rare cases in the sump region of a PWR nuclear power plant, because the direct environment of the inlet openings of the suction ducts is constructed in such a way that it is unsuitable for the use of cylindrical suction screens. A suction space for the installation of protective screen elements with a suitable screen area is mainly provided in front of the inlet openings of the suction ducts. For space reasons the suction space in the sump region of a PWR nuclear power plant is, on average, relatively shallow.